From 84d1427cab3c74b1f5082c304b5282cb1f685372 Mon Sep 17 00:00:00 2001
From: Geoffrey McRae <geoff@hostfission.com>
Date: Tue, 4 Aug 2026 13:48:23 +1000
Subject: [PATCH] [idd] make mode filtering rebuilds thread safe

---
 idd/LGIdd/CIndirectDeviceContext.cpp |  7 ++++---
 idd/LGIdd/CSettings.cpp              | 17 +++++++++--------
 idd/LGIdd/CSettings.h                |  7 ++-----
 3 files changed, 15 insertions(+), 16 deletions(-)

diff --git a/idd/LGIdd/CIndirectDeviceContext.cpp b/idd/LGIdd/CIndirectDeviceContext.cpp
index f3580632..edbc20eb 100644
--- a/idd/LGIdd/CIndirectDeviceContext.cpp
+++ b/idd/LGIdd/CIndirectDeviceContext.cpp
@@ -148,20 +148,21 @@ void CIndirectDeviceContext::QueryIddCxCapabilities()
 
 bool CIndirectDeviceContext::PopulateDefaultModes()
 {
-  g_settings.LoadModes();
+  const CSettings::DisplayModes configuredModes =
+    g_settings.LoadModes();
 
   // Build the new mode list into a local first so we only hold the lock for
   // the swap. IddCx readers may be iterating the live container on another
   // thread; a clear()/push_back() under them would reallocate the backing
   // store and crash. std::move makes the publish a pointer swap.
   CSettings::DisplayModes newModes;
-  newModes.reserve(g_settings.GetDisplayModes().size());
+  newModes.reserve(configuredModes.size());
 
   const UINT64 alignment = m_alignSize ? m_alignSize :
     D3D12_DEFAULT_RESOURCE_PLACEMENT_ALIGNMENT;
 
   bool hasPreferred = false;
-  for (const auto& configuredMode : g_settings.GetDisplayModes())
+  for (const auto& configuredMode : configuredModes)
   {
     UINT64 frameSize;
     UINT64 requiredIVSHMEMSize;
diff --git a/idd/LGIdd/CSettings.cpp b/idd/LGIdd/CSettings.cpp
index 312ddd74..ae3bd03c 100644
--- a/idd/LGIdd/CSettings.cpp
+++ b/idd/LGIdd/CSettings.cpp
@@ -32,24 +32,24 @@ CSettings::CSettings()
 {
 }
 
-void CSettings::LoadModes()
+CSettings::DisplayModes CSettings::LoadModes()
 {
   const unsigned defaultRefresh = GetDefaultRefresh();
-  m_displayModes.clear();
+  DisplayModes displayModes;
 
   bool hasPreferred = false;
   DisplayMode m;
   if (GetExtraMode(m))
   {
     DEBUG_INFO("ExtraMode: %ux%u@%u%s", m.width, m.height, m.refresh, m.preferred ? "*" : "");
-    m_displayModes.push_back(m);
+    displayModes.push_back(m);
     hasPreferred = m.preferred;
   }
 
   std::vector<std::wstring> entries;
   if (!ReadModesValue(entries))
   {
-    m_displayModes.reserve(m_displayModes.size() +
+    displayModes.reserve(displayModes.size() +
       ARRAYSIZE(DefaultDisplayModes));
 
     for (int i = 0; i < ARRAYSIZE(DefaultDisplayModes); ++i)
@@ -59,9 +59,9 @@ void CSettings::LoadModes()
       m.refresh   = defaultRefresh;
       m.preferred = !hasPreferred && (i == DefaultPreferredDisplayMode);
       m.extraMode = false;
-      m_displayModes.push_back(m);
+      displayModes.push_back(m);
     }
-    return;
+    return displayModes;
   }
 
   for (const auto& line : entries)
@@ -69,10 +69,11 @@ void CSettings::LoadModes()
     {
       if (hasPreferred)
         m.preferred = false;
-      m_displayModes.push_back(m);
+      displayModes.push_back(m);
     }
 
-  DEBUG_INFO("Parsed %d modes", m_displayModes.size());
+  DEBUG_INFO("Parsed %d modes", displayModes.size());
+  return displayModes;
 }
 
 void CSettings::SetExtraMode(const DisplayMode& mode)
diff --git a/idd/LGIdd/CSettings.h b/idd/LGIdd/CSettings.h
index a391da52..f31a763e 100644
--- a/idd/LGIdd/CSettings.h
+++ b/idd/LGIdd/CSettings.h
@@ -38,8 +38,7 @@ class CSettings
 
     CSettings();
 
-    void LoadModes();
-    const DisplayModes& GetDisplayModes() { return m_displayModes; }
+    DisplayModes LoadModes();
     void SetExtraMode(const DisplayMode & mode);
     bool GetExtraMode(DisplayMode & mode);
     unsigned GetDefaultRefresh() const;
@@ -48,10 +47,8 @@ class CSettings
     bool ReadBoolValue(const wchar_t* name, bool defaultValue = false);
 
   private:
-    DisplayModes m_displayModes;
-
     bool ReadModesValue(std::vector<std::wstring> &out) const;
     bool ParseModeString(const std::wstring& in, DisplayMode& out);
 };
 
-extern CSettings g_settings;
\ No newline at end of file
+extern CSettings g_settings;